This invention relates generally to the operation of optical media player and recorder machines, such as those that operate with both compact disc (CD) and digital versatile disc (DVD) types, and, more specifically, to techniques for reliably identifying the type of disc that has been placed into such a machine.
After an optical data disc is placed into a player or recorder, one of the first operations automatically performed by the machine is to identify the type of the disc by its physical characteristics. A common identification technique measures the relative distance from a surface of the disc to a reflective layer within the disc where the data are stored. One way this is done is to move the focal point of the optical pick-up unit into the disc and measure the amount of time elapsed between photodetector output signals of reflections from the outer surface and then from the data layer within the disc. Different types of media have their data surfaces positioned at different distances from their outer surfaces. This surface in CDs is nominally twice the distance from an outside surface as in DVDs, for example.
This initial disc identification is necessary for the machine to next configure and calibrate itself to operate with that particular type of disc. Differences between types of discs include the data track spacing, the position of the data containing layer within the disc, the physical format of the data stored on the disc tracks, the protocol of the stored data, and the like. If the disc is improperly identified, an initial attempt to complete a calibration phase or read the data may fail. The machine then usually either repeats the identification process, or tries to configure itself to operate with some other type of disc, or sometimes both. This process usually takes a significant amount of time, which is typically unacceptable to the user of a machine.